The UK contribution to CTA

Transcription

1 The UK contribution to CTA Introduction The dual mirror SST SST-GATE and ASTRI telescopes A camera for the dual mirror SST Overview Sensor, pre-amp, TARGET ASIC and module Enclosure, cooling, DAQ and peripherals Summary

2 SST: science goals and requirements Design philosophy SST requirements driven both by CTA s science goals E.g. locating and studying PeVatrons requires SST array sensitive from ~1 300 TeV with good energy (~10%) and angular (~0.03 ) resolution. and by the limitations imposed by the site, by safety considerations etc. SST must operate in winds with 10 minute average speed, at 10 m height, of up to 36 km/h. In park position, SST must survive 10 minute average wind speed of up to 120 km/h. High energy sensitivity requires SSTs cover large area...but telescope separation cannot be too large (want many images of each shower). Need lots of SSTs: low cost essential. Could use small MST with D = 7 m, F = 11.2 m and PM camera 2

3 The CTA concept, take one Low energy Four 23 m telescopes 4 5 o FoV ~2000 pixels ~ 0.1 o Medium energy About twenty-five 12 m telescopes 6 8 o FoV ~2000 pixels ~ 0.18 o High energy About forty 7 m telescopes 8 10 o FoV Camera diameter ~2 m ~2000 pixels ~ 0.23 o

4 Towards a two-mirror SST but this is expensive, cost dominated by camera: large number of expensive PMs needed. Cheaper camera possible? UK proposal: switch to using relatively low cost compact sensors. Need more sophisticated (two-mirror) optical system to reduce aberrations at large field angles. Can then have small pixels across large field of view. (Two mirror telescopes first proposed in US for AGIS, will also be used for SCT in CTA.) First studies of dual mirror SST optics carried out in UK, e.g. ray tracing for field angles 0, 2.5, 5 : 4

5 PSF (m) Towards a two-mirror SST Results of UK optimisation procedure, is telescope with: Focal length F = m. Primary diameter D P = 4 m. Secondary diameter D S = 2 m. Camera diameter D C = 0.36 cm. Distance from primary (M1) to secondary mirror (M2) 3.56 m. Distance from M2 to camera is 0.51 m. Radius of 2 max curvature revupsf3 Nc of camera 10 3 r C = 1 m. 2 revupsf3 nc Resulting point spread functions: Field angle ( ) degt nc Image size less than 6 mm diameter (80% of light) across entire 9 field of view. 5

6 Towards a two-mirror SST Range of sensors available: Microchannel plates. First UK mechanical design: Silicon photomultipliers (SiPMs). Multianode photomultipliers MAPMs. Demonstrated feasibility of two mirror solution. 6

7 The CTA concept, take two Low energy Four 23 m telescopes 4 5 o FoV ~2000 pixels ~ 0.1 o Medium energy About twenty-five 12 m telescopes 6 8 o FoV ~2000 pixels ~ 0.18 o High energy About seventy 4 m telescopes 8 10 o FoV pixels ~ 0.17 o 0.23 o

8 SST-GATE telescope Mechanical design further pursued by French groups 8

9 ASTRI telescope and by Italian consortium. F = 2.15 m, D P = 4.3 m. Gives f = F/D P = 0.5. D S = 1.8 m, distance M1 to M2 is 3 m. D C = 36 cm, FoV = 9.6, r C = 1 m. PSF: D 80 < 6 mm over entire FoV. 9

10 UK project a camera for the SST-2M Sensors: Micro-channel plates: predicted lifetime about 10 6 secs (300 hrs). MAPMs: reasonably priced 64 pixel units available from Hamamatsu. SiPMs: growing range of devices, costs now competitive with PMs. Design camera to use either MAPMs (CHEC-M) or SiPMs (CHEC-S) with a pixel size of ~ 6 6 mm 2 and which can be used on either SST-2M telescope design. Collaborate with US groups. Use TARGET ASIC and module, designed to readout MAPMs for AGIS, now also being used for SCT SiPM-based camera. 10

11 CHEC overview Chilled Block Chilled Liquid Thermal Control Fans Low Voltage Backplane Communications Photosensor Modules Camera Controller Peripherals Control LED Flashers, Pointing LEDs Preamplifier Module Target Module Enclosure, Lid 11

12 64 pixel sensor Backplane Board Backplane 64 pixel sensor CHEC overview Buffering and serialisation 16 Preamps 16 Preamps 1 x Preamps 16 x preamp Target Asic Target Asic Target Asic TARGET ASIC TARGET Module FPGA Data Camera trigger Any two super-pixel neighbours Trigger x 32 Amplification and shaping Digitisation and trigger Clock Module trigger 6 mm (0.17 ) MAPM pixel Peripherals (calibration, lid ) 0.34 super-pixel DACQ Boards Control signals, data Data serialisation and control 12

13 TARGET module with MAPM Four 16 channel preamp boards Four ribbon cables HV Connection to backplane TARGET ASIC 13

14 Preamp MAPM output pulse width ~ 1 ns. Less than spread of Cherenkov photon arrival times: stretch pulse to form module trigger. Design shaping pre-amplifier, requirements: Dynamic range < 1 ~1000 p.e. 0 ~1.2 V. Noise < 0.5 mv. Rise time ~ 4 ns. Pulse width ~ 8 ns. Pre-amp output for small and large signals. Saturation (~1000 PE, combination of preamp and MAPM) 14

15 Preamp Module CHEC-M Preamplifier Signal patching board 50-Ohm flex-cables (shielded) Focal plane interface Amplifier boards MAPM or SiPM Target Interface HV Bias 15

16 TARGET module/pre-amp testing 16

17 TARGET module testing 17

18 Backplane Must allow inter-module triggering. Signals from all modules must be provided to FPGA. Layout of board now being carried out in US (collaboration with Washington University). 18

19 Camera support structure Enclosure: Internals: 19

20 Camera support structure Faceplate: Lid: 20

21 Cooling Water cooled heat exchanger in camera enclosure with fans to circulate air within camera. External chiller, placed on ground adjacent to telescope. 21

22 Camera calibration Flat fielding and other calibration operations aided by LED unit in corners of camera. Light reflected off M2 onto sensor plane 22

23 Peripherals control DAQ power-on/reset, 4 fans, 6 temp sensors, 2 motors, 2 micro-switches, position encoder, ambient light sensor, 4 calibration flashers are all controlled by peripherals board. E.g. flasher steering curcuitry: Flasher output signal (measured using TARGET module). Pulse width < 4.5 ns. Similar to duration of Cherenkov light flashes camera must measure. 23

24 DAQ DAQ board routes 32 TARGET module signals to (remote) camera server over optical fibre. Generates clock. Handles time-stamping of data. Steers communication with housekeeping FPGA. Prototype: Virtex 6 FPGA, Seven Solutions White Rabbit switch. Test board for prototype: 24

25 SiPMs Test range of devices that are currently on the market, including. Excelitas C mm cells. 6 6 mm 2 pixels. Hamamatsu S CN. 50 mm cells. Through Si vias. 3 3 mm 2. SensL MicroFB-SMA mm cells. Fast output. 6 6 mm 2 pixels. For CHEC-S prototype, will use Hamamatsu SiPM. New pre-amp and some redesign of mechanical structure of camera required. 25

26 Timescale for prototype tests CHEC-M prototype ready Autumn Test on SST-GATE telescope in Paris and on ASTRI telescope on Etna. CHEC-S ready for testing mid Design final camera and start production mid

27 Summary UK groups initiated discussion of twomirror design for the SST. Showed potential for significant cost saving w.r.t. initial CTA concept. Produced first optical and mechanical design of two-mirror telescope. Prototype telescopes now under construction in France and Italy. UK producing camera for these telescopes, in collaboration with Australian, Dutch, Japanese and US groups. Ambition is to build cameras at cost of ~ 100k each. Welcome discussion on possible industry participation in this project. 27